The invention concerns an agitator for the mixing and/or conveying of aggressive liquids and/or liquids containing solids or fibers, consisting of a drive motor which is encapsulated by a housing and seals so as to be liquid-tight, on the central drive shaft of which a propeller boss is located, the largest diameter of which is roughly equal to the diameter of the housing, where an elastic deflector ring which overlaps the gap between propeller boss and housing is provided on the housing.
This class of drive, as known from U.S. Pat. No. 5,007,867 or EP-A-0.252.037, for example, is also used as agitators, particularly in sewage engineering, for mixing liquids containing solids or fibers, in order to prevent the solids settling on the bottom of a tank or container, for example. To this end, the agitators are immersed in the liquid to be mixed and fastened below the liquid level. The liquids to be mixed can, to a limited extent, also be conveyed with the help of the agitators if an appropriate piece of piping is installed upstream of the propeller.
The usually dome-shaped design of the propeller boss, the largest diameter of which is roughly equal to the diameter of the housing, is intended to achieve the most favorable flow conditions possible, in order to keep the formation of eddies relatively low and achieve an optimum mixing effect at a high level of efficiency.
According to the prior art, in order to avoid solid or fibrous materials being drawn into the gap between the housing and the propeller boss in the known drives or agitators, a deflector ring is placed over this gap, but does not lie against the propeller boss to form a seal.
In addition to the penetration of solid materials, there is also the problem, when handling aggressive liquids, that acids or alkalis with relatively high flow rates pass through the gap into the internal cavity of the propeller boss and act on the drive shaft or the floating ring seals surrounding the drive shaft, which can cause damage or leaks. In order to prevent the penetration of such aggressive liquids, attempts have thus been made to build up excess pressure with the help of a rinsing liquid which is fed into the internal cavity of the propeller boss so that the aggressive liquids can no longer enter or are diluted. However, as this liquid escapes through the gap, relatively large quantities of rinsing liquid must be used.